1. Field of the Invention
The present invention relates to a recording/playback apparatus.
2. Description of the Related Art
There is a system which is provided with an in-cassette memory for recording information regarding recording contents or the like and a cassette-side antenna and in which access is gained to the in-cassette memory while keeping the recording/playback apparatus side in a non-contact state.
When reducing the size of a recording/playback apparatus, it is necessary, from the viewpoint of strength, that the cassette holding member, which holds the recording medium cassette and which moves between the recording/playback position where recording and/or playback is effected to and from the recording medium cassette and the cassette passing position where the passing of the recording medium cassette is effected between the interior and the exterior of the apparatus, must be formed of a metal.
FIG. 14 shows an example of a coil pattern formed on a printed circuit board. As shown in FIG. 14, the coil formed on the printed circuit board is realized by spirally developing the pattern on the printed circuit board from a terminal (input terminal) a1 on one side of the coil connected to a tap 211 toward the inner periphery side.
Here, when an attempt is made to connect a terminal (output terminal) b1 on the opposite side of the terminal a1 to a tap 213, it is impossible to lead out the pattern from the side (side A) where the pattern forming the coil is developed (In the same plane, it is impossible for one pattern to jump over the other pattern so that the two patterns may not come into contact with each other), so that it is necessary to lead out the pattern from a terminal a2 of the coil of the side A to the opposite side (side B) through a through-hole, and to form on the side B a pattern indicated by a dashed line, connecting the pattern to the terminal b1 through the through-hole. That is, it is necessary to form the printed circuit board 1 as a two-layer (double-sided) substrate. Further, in this case, by connecting terminals c2 and c1 in the intermediate portion of the coil by utilizing the side B, it is possible to prepare a tap 212.
To keep the substrate area small while improving the inductance of this coil, a spiral pattern is formed on either of the sides A and B of the double-layer substrate, as in the case of a printed circuit board 220 shown in FIG. 15 (That is, the number of turns of the coil is increased). However, in the case of FIG. 15, while taps 221 and 222 connected to both ends of the coil can be easily formed, it is impossible, due to the fact that it is a pattern on a substrate, to form an intermediate tap unless air wiring (for example, wiring using a jumper line).
Thus, if an improvement in inductance is to be achieved with a small substrate area, and further, if an intermediate tap is to be provided, another layer is added to form a three-layer structure to form a pattern for the intermediate tap on the printed circuit board, whereby, as in the case of a printed circuit board 230 shown in FIG. 16, it is possible to mount taps 231 through 233 without performing air wiring. In the case of the example shown in FIG. 16, an intermediate terminal a2 is formed between the input terminal a1 connected to the tap 231 and the output terminal b1 connected to the tap 233, and this intermediate terminal a2 is connected to the tap 232 through the terminal c1.
When a coil formed on a substrate is used, for example, in a circuit of an antenna used in radio communication, electromagnetic coupling non-contact communication or the like, the power last step circuit on the transmission side is in many cases formed as a push-pull circuit, and, to supply transmission power to the coil, it is more advantageous that an intermediate tap be formed in the coil. FIG. 17 shows an example of a coil of a transmission apparatus using a coil having no intermediate tap (the printed circuit board 220 described with reference to FIG. 15) in electromagnetic coupling non-contact communication.
Drive signals of normal and reverse phases are emitted by signal sources V1 and V2 in FIG. 17. These signals are increased in power by transistors Q1 and Q2 and resonated at a predetermined communication frequency by a capacitor C3. The values of capacitors C1 and C2 and resistors R1 through R7 are determined by the characteristics of the circuit. The DC voltage applied to the collectors of the transistors Q1 and Q2 is supplied through choke coils L1 and L2, and the connection point of the choke coils L1 and L2 undergoes decoupling by a choke coil L3 and a capacitor C2. The radiation of the output signal is maximum in a direction perpendicular to the printed circuit board 2. Further, transistors Q3 and Q4 are used for the purpose of buffering.
There is a technique, as shown in FIG. 24, in which signals are transmitted and received in a non-contact state between a communication apparatus 301 having an antenna 303 and a communication apparatus 302 having an antenna 304 by utilizing the electromagnetic coupling generated between the antennas 303 and 304. When the antennas 303 and 304 of the communication apparatuses 301 and 302 consist of ordinary RCL circuits, as shown in FIG. 25, the equivalent circuits of the antennas 303 and 304 are as shown in FIG. 26. The communication conducted between the antennas 303 and 304 is effected by the mutual inductance M.
Impedances Z1 through Z5 in FIG. 26 are as follows: Z1 corresponds to the impedance 1/jωC1 of the capacitor C1 of the antenna 303; Z2 corresponds to the synthetic impedance R1+jω(L1−M) consisting of the resistance R1 of the antenna 301 and the inductance L1−M obtained by subtracting the mutual inductance M from the inductance L1; Z3 corresponds to the impedance jωM corresponding to the mutual inductance M; Z4 corresponds to the synthetic impedance R2+Jω(L2−M) consisting of the resistance of the antenna 2 and the inductance L2−M obtained by subtracting the mutual inductance M from the inductance L2; and Z5 corresponds to the impedance 1/jωC2 of the capacitor C2 of the antenna 302.
In the circuit shown in FIG. 26, assuming that the current flowing through the impedance Z2 is i1 and that the current flowing through the impedance Z5 is i2, the currents i1 and i2 can be expressed by the following formulas 1 and 2.i1=−SEin×Z1/{Z1+Z2+Z3(Z4+Z5)/(Z3+Z4+Z5)}  (1)i2=i1×Z3/(Z3+Z4+Z5)  (2)                Here, S indicates the mutual susceptance of the amplifier driving the antenna 301. Thus, −SEin indicates the total current of the circuit.        
And, the voltage E2 applied to both ends of the antenna 302 is expressed by the following formula 3.E2=i2×Z5=i1×Z3×Z5/(Z3+Z4+Z5)  (3)
From formulas 1 through 3, the reciprocal of amplification degree D, which is the inverse number of the amplification degree G, is obtained as shown by the following formula 4.D=1/G=Ein/E2={−1/(S×Z1×Z3×Z5)}×{(Z1+Z2+Z3)(Z3+Z4+Z5)−Z32}  (4)
Here, assuming that both the primary circuit and the secondary circuit are resonating, the resonance frequency ωO is expressed by the following formula 5.ω0=1/√{square root over (L1C1)}=1/√{square root over (L2C2)}  (5)
And, the voltage E2 applied to both ends of the antenna 302 is expressed by the following formula 3.E2=i2×Z5=i1×Z3×Z5/(Z3+Z4+Z5)  (3)From formulas 1 through 3, the reciprocal of amplification degree D, which is the inverse number of the amplification degree G, is obtained as shown by the following formula 4.D=1/G=Ein/E2={−1/(S×Z1×Z3×Z5)}×{(Z1+Z2+Z3)(Z3+Z4Z5−Z32}  (4)
Here, assuming that both the primary circuit and the secondary circuit are resonating, the resonance frequency ωO is expressed by the following formula 5.ω01/√{square root over (L1C1)}=1/√{square root over (L2C2)}  (5)
And, assuming that the coupling coefficient is k, k is expressed by the following formula 6 from the values of the mutual inductance M and the inductance L1 and the inductance L2 of the antenna 301 and the antenna 302.
Further, assuming that the Q (quality factor) at the time of resonance is Q1 in the primary circuit and Q2 in the secondary circuit, Q1 and Q2 are expressed by the following formulas 7 and 8.Q1=(ωOL1/R1  (7)Q2=(ωOL2/R2  (8)
Thus, assuming that the loss factor d is d1 in the primary circuit and d2 in the secondary circuit, the loss factor d1 and the loss factor d2 are expressed by the following formulas 9 and 10.d1=1/Q1  (9)d2=1/Q2  (10)
Assuming that the detuning factor indicating the difference between the actual communication frequency ω and the resonance frequency ωO is x, the detuning factor x is expressed by the following formula 11.x=(ω−ωO)/ωO  (11)
Here, it is the proximity to the resonance point that is in question, so that the following formula 12 holds true.ω≈ω0  (12)
Thus, by substituting formulas 5 through 12 into formula 4 and performing arrangement, formula 13 is obtained.
                    D        =                                            -              j                                      s              ⁢                                                          ⁢                              ω                0                            ⁢                                                                    L                    1                                    ⁢                                      L                    2                                                                                ×                      1            k                    ⁢                      {                                                            (                                                            d                      1                                        +                                          2                      ⁢                      jx                                                        )                                ⁢                                  (                                                            d                      2                                        +                                          2                      ⁢                      jx                                                        )                                            +                              k                2                                      }                                              (        13        )            
Here, regarding the frequency characteristics of the reciprocal of amplification gain, the absolute value of 1/k{(d1+j2x){d2+j2x}+k2}, which is the variable portion of formula 12, is to be considered, so that the following formula 14 is used as the frequency characteristics of the reciprocal of amplification gain y.
                    y        =                              1            k                    ⁢                                                    16                ⁢                                  x                  2                                            -                              4                ⁢                                  (                                                            2                      ⁢                                              k                        2                                                              -                                          d                      1                      2                                        -                                          d                      2                      2                                                        )                                ⁢                                  x                  2                                            +                                                (                                                            k                      2                                        +                                                                  d                        1                                            ⁢                                              d                        2                                                                              }                                2                                                                        (        14        )            
The maximum point and the minimum point at the point of inflection of the frequency characteristics (communication efficiency) are points at which dy/dx=0 in formula 14, so that the maximum point is expressed by the following formulas 15 and 16, and the minimum point is expressed by the following formulas 17 and 18.x0=0  (15)y0=(k2+d1d2)/k  (16)
                              x          b                =                              ±                          1              2                                ⁢                                                                      2                  ⁢                                      k                    2                                                  -                                  (                                                            d                      1                      2                                        +                                          d                      2                      2                                                        )                                            2                                ⁢                                          ⁢                      (                          1              ≥              k              ≥                                                                                          d                      1                      2                                        ⁢                                                                                  ⁢                                          d                      2                      2                                                        2                                                      )                                              (        17        )                                          y          b                =                                                            d                1                            +                              d                2                                                    2              ⁢              k                                ⁢                                                    4                ⁢                                  k                  2                                            -                                                (                                                            d                      1                                        -                                          d                      2                                                        )                                2                                                                        (        18        )            
Further, the optimum coupling coefficient kO providing the maximum gain (that is, at the time of critical coupling) is k, which provides the relationship dy0/dk=0 when formula 16 is differentiated with respect to k, so that the optimum coupling coefficient k0 is expressed by formula 19.ko=√{square root over (d1d2)}=1/√{square root over (Q1Q2)}  (19)
The yO at that time can be obtained by substituting formula 19 into formula 16. Formula 20 shows the value of yO at the time of critical coupling.y0=2√{square root over (d1d2)}  (20)
Thus, the gain GO is expressed by formula 21.
                              G          o                =                              s            ⁢                                                  ⁢                          ω              o                        ⁢                                                            L                  1                                ⁢                                  L                  2                                ⁢                                  Q                  1                                ⁢                                  Q                  2                                                              2                                    (        21        )            
Assuming that the antenna 303 and the antenna 304 are of the same performance, d1=d2 =d=kO and y0=yb=2d.
FIG. 27 shows the transfer frequency characteristic y when, in formula 11, the coupling coefficient k is k<kO, k=kO, and k>kO. It can be seen from FIG. 27 that when the coupling coefficient k satisfies the relationship k<kO, y exhibits a single peak characteristic, and as k approaches kO, the value of y when x=0 decreases. When k>kO, the transfer frequency characteristic y from the antenna 303 to the antenna 304 changes from the single peak characteristic to a wavy (double peak) characteristic, and the maximum value of the communication efficiency (that is, the minimum value of the transfer frequency characteristic y) at the time of critical coupling (k=kO) is the same as that at the time of wavy characteristic (k>kO). Further, the voltage value E1 of the antenna 1 exhibits substantially the same characteristic. As can be seen from these facts, the critical coupling point kO being the border, even when k decreases, the passing range center frequency level decreases, and the communication efficiency deteriorates. That is, it can be seen that communication is difficult to perform when the non-contact distance (inter-antenna distance) is too small or too large.
The inter-antenna coupling coefficient k is determined by the antenna configuration, the relative distance, etc., while, as shown in formula 19, the critical coupling condition kO is determined by the Q1 and the Q2 of the antenna 303 and the antenna 304. Thus, by adjusting the Q of the antenna, it is possible to some degree to control the transfer frequency characteristic, for example, whether the transfer frequency at a certain coupling coefficient k exhibits a single peak characteristic or a wavy characteristic. That is, by effecting binary variation of the value of this Q in accordance with the information to be transmitted, it is possible to effect transmission and reception of information between the antennas by utilizing ASK (amplitude shift keying).
Generally speaking, as compared with the communication apparatus 301, the communication apparatus 2 is devoid of a power source and retains the spreading of the ASK band and rectifies a high-frequency signal to utilize it as the power source for itself, so that the degree of modulation is set to be low modulation. When information is transferred from the communication apparatus 2 to the communication apparatus 301, the Q2 of the antenna 304 is equivalently varied in accordance with the information to be transmitted, so that the resistance R2 of the antenna 304 is turned ON/OFF (FIG. 25). When information is transmitted from the communication apparatus 301 to the communication apparatus 2, the circuit current value of the antenna 303 is varied in accordance with the information to be transmitted. The mutual communication is performed on a time division basis (semi-double system). While the communication apparatus 301 is transmitting a signal, the Q2 of the communication apparatus 302 is fixed, and while the communication apparatus 302 is transmitting a signal, the circuit current value of the communication apparatus 301 is fixed.
FIG. 28 shows the transfer frequency characteristic (the output voltage with respect to the communication frequency) when the resistance R2 of FIG. 25 is turned OFF when the information signal bit is 0 and turned ON when the information signal bit is 1. When the carrier signal frequency is in the proximity to 13.56 MHz (point c), a signal exhibiting an amplitude variation corresponding to the turning ON/OFF of the resistance R2 is supplied to the antenna 303 of the communication apparatus 301. The difference in this transfer amplitude is the ASK signal obtained at the communication apparatus 301. Although in this case, a binary variation is achieved through a combination of the wavy characteristics, it is possible, in some cases, to achieve a binary variation through a combination of a wavy characteristic and a single-peak characteristic.
Incidentally, when a recording medium cassette is held by a cassette holding member, if there is a metal portion in the portion opposed to the cassette-side antenna, the radio wave is not propagated in a satisfactory manner even if the recording/playback-apparatus-side, i.e., the apparatus-side antenna, is opposed to the cassette-side antenna, so that the communication cannot be performed in a satisfactory manner.
Further, when the size of the recording/playback apparatus is to be reduced, the cassette holding member has to be formed of a metal from the viewpoint of strength.